Heretofore, as a working fluid for heat cycle such as a refrigerant for a refrigerator, a refrigerant for an air-conditioning apparatus, a working fluid for a power generation system (such as exhaust heat recovery power generation), a working fluid for a latent heat transport apparatus (such as a heat pipe) or a secondary cooling fluid, a chlorofluorocarbon (CFC) such as chlorotrifluoromethane or dichlorodifluoromethane or a hydrochlorofluorocarbon (HCFC) such as chlorodifluoromethane has been used. However, influences of CFCs and HCFCs over the ozone layer in the stratosphere have been pointed out, and their use is regulated at present.
Under the above conditions, as a working fluid for heat cycle, a hydrofluorocarbon (HFC) which has less influence over the ozone layer, such as difluoromethane (HFC-32), tetrafluoroethane or pentafluoroethane (HFC-125) has been used, instead of CFCs and HCFCs. For example, R410A (a pseudoazeotropic mixture fluid of HFC-32 and HFC-125 in a mass ratio of 1:1) is a refrigerant which has been widely used. However, it is pointed out that HFCs may cause global warming.
R410A has been widely used for a common air-conditioning apparatus such as a so-called package air-conditioner or room air-conditioner, due to its high refrigerating capacity. However, it has a global warming potential (GWP) of so high as 2,088, and accordingly development of a working fluid with low GWP has been desired.
Accordingly, in recent years, a hydrofluoroolefin (HFO) i.e. a HFC having a carbon-carbon double bond is expected, which is a working fluid having less influence over the ozone layer and having less influence over global warming, since the carbon-carbon double bond is likely to be decomposed by OH radicals in the air. In this specification, a saturated HFC will be referred to as a HFC and distinguished from a HFO unless otherwise specified. Further, a HFC may be referred to as a saturated hydrofluorocarbon in some cases. Further, abbreviated names of halogenated hydrocarbon compounds such as HFCs and HFOs are described in brackets after the compound names, and in this specification, the abbreviated names are employed instead of the compound names as the case requires.
As a working fluid employing a HFO, for example, Patent Document 1 discloses a technique relating to a working fluid using trifluoroethylene (HFO-1123) which has the above properties and with which excellent cycle performance will be obtained. Patent Document 1 also discloses an attempt to obtain a working fluid comprising HFO-1123 and various HFCs in combination for the purpose of increasing the flame retardancy, cycle performance, etc. of the working fluid.
Here, HFO-1123 is known to undergo self-decomposition at high temperature or with an ignition source under high pressure when used by itself. Therefore, Non-Patent Document 1 reports an attempt to suppress self-decomposition reaction by mixing HFO-1123 with another compound such as vinylidene fluoride to form a mixture having a lowered content of HFO-1123.
Further, as the HFO to be used for the working fluid for heat cycle, 2,3,3,3-tetrafluoropropene (HFO-1234yf) is known to be useful, and a technique relating to HFO-1234yf is under development. For example, Patent Document 2 discloses a composition containing HFO-1234yf obtained in production of HFO-1234yf by a specific method. The composition disclosed in Patent Document 2 includes many compounds, and a composition containing HFO-1234yf and HFO-1123 is included. However, HFO-1123 is only disclosed together with many other compounds as a by-product of HFO-1234yf, and use of a composition comprising HFO-1234yf and HFO-1123 mixed in a specific proportion as a working fluid is not disclosed.